1. Field of the Invention
Disclosed are polyester-ether polyols and methods for producing such polyester-ether polyols employing a double metal cyanide catalyst, along with urethane prepolymers and methods for producing urethane prepolymers comprising the polyester-ether polyols. Such polyols and urethane prepolymers are useful in the preparation of urethane foams and/or non-foam urethanes, wherein the polyester-ether polyol is either the primary polyol component or is utilized in combination with conventional auxiliary polyester- and/or polyether-based polyols. The invention further relates to urethane foam and non-foam urethane compositions such as coatings, adhesives, sealants, and elastomers, which may be prepared utilizing the polyester-ether polyols and/or the urethane prepolymers derived therefrom. The polyols of the instant invention are preferably the reaction product of phthalic anhydride and diethylene glycol, to produce an intermediate polyester polyol, which is subsequently reacted with an alkylene oxide, e.g., propylene oxide, in the presence of a double metal cyanide catalyst, e.g., a zinc hexacyanometallate and in particular a zinc hexacyanocobaltate, to produce the subject polyester-ether polyols. These polyester-ether polyols impart greatly improved solubility and compatibility to or with mixtures of known alkylene oxide polyols (e.g., polypropylene oxide based polyether polyols) and polyester polyols. The polyester-ether polyols of the instant invention are desirably of lower viscosity than precursor polyester polyols and are generally soluble in either polyester- and/or polyether-based polyols.
2. Description of the Related Art
Desirable physical properties of non-foam polyurethane coatings, adhesives, sealants and elastomers (CASE) include, among others, durability, flexibility, rigidity, hardness, toughness, resistance to abrasion, ability to bond to various substrates, and resistance to chemicals; one of the most desirable properties is hydrolytic stability. Coatings, adhesives, sealants and elastomers which are not resistant to hydrolysis undergo chain scission and gradual degradation of the other physical properties. Desirable properties of finished urethane foams include beneficial insulation characteristics and flame retardency. Industrial polyurethanes are generally made from the reaction of isocyanates/polyisocyanates and materials with multiple hydroxyl moieties (“polyols”). In many foam, adhesive and coatings formulations, polyols comprise the majorty of the formulation weight, so that the final product properties are influenced mostly by the polyols.
Of the commercially available polyols, polyether- and polyester-containing materials are dominant. Polyether polyols are usually based on propylene oxide, ethylene oxide or tetrahydrofuran. These typically exhibit very good resistance to hydrolysis, which is an important requirement of many adhesives and coatings. However, polyether polyols promote adhesion to a very limited variety of substrates. In contrast, polyester polyols generally promote adhesion to more types of surfaces but are more susceptible to hydrolysis. Typically, a polyester molecule is hydrolyzed to an acid and alcohol as shown below. The hydrolysis may be acid or base catalyzed. The deleterious consequence of such hydrolysis in a polyurethane material is the loss of desirable physical properties, as hydrolysis gives undesirable products with lower molecular weight.
In addition, polyester polyols are utilized in both foam and nonfoam formulations to improve physical properties such as toughness, tensile and flexural strength, durometer hardness, solvent resistance, and thermal properties. Urethane coatings, and other applications, based on polypropylene oxide polyols and toluene diisocyanate have found limited applications, i.e. indoors only, as also they contain contaminant ether linkages which are readily prone to oxidative degradation. CASE materials derived from polyester polyols, such as those prepared by the condensation of an aliphatic dicarboxylic acids and poly alcohols, are widely used indoors and outdoors. Their primary function in finished CASE materials has been to enhance abrasion resistance. While these CASE materials possess better durability than those based on polypropylene oxide polyols and toluene diisocyanate, they also contain ether groups that undergo oxidative degradation.
Aliphatic polyester polyols, which contain ether linkages and/or ester linkages have found wide spread use in CASE, as additives which can provide improved bonding and durability. These materials are generally based on caprolactone or adipic acid backbones. One of the more widely used commercial polyester polyols is based on polycaprolactone and sold under the trade name Tone® (Union Carbide Corp.). This polyester polyol is the product of the homopolymerization of caprolactone with a hydroxyl containing compound as an initiator, such as a diol, to form polycaprolactone polyols. These polyester polyol materials are hydrolytically stable, resistant to yellowing, display excellent abrasion, chemical and impact resistance, they provide excellent resistance to oxidative degradation, and are considered to be the leaders of the commercial products which are currently available. However, such materials are generally of high molecular weight (i.e., 1000 g/mol), they are solids at about 25° C. which require heating (to about 60° C.) prior to use and they are therefore generally more difficult to formulate with as compared to lower melting, lower viscosity polyols.
Aliphatic polyester polyols based on adipic acid are prepared by the condensation of adipic acid and a diol, such as 1,6-hexanediol, as shown below:HO2C—(CH2)4—CO2H+HO—(CH2)6—OH→HO[—(CH2)6—OOC—(CH2)4—COO—](CH2)6—OHThese materials are well known to undergo hydrolytic degradation at the ester linkage cites of the molecule. However, the materials have the advantage of a low manufacturing cost, as compared to Tone® type materials, which is favorable from a consumer point of view.
Polyester polyols derived from phthalic anhydride (PA) and low molecular weight diols are reported in U.S. Pat. No. 4,644,027 to Magnus et al., issued Feb. 17, 1987 and U.S. Pat. No. 4,644.047 to Wood, issued Feb. 17, 1987, for the production of cellular polyurethane and polyurethane/polyisocyanates. Polyester polyols derived from PA and neopentyl glycol have been reported in U.S. Pat. No. 4,390,688 to Walz et al., issued Jun. 28, 1983. These materials are described as water dilutable polyesters with good resistance to xylene and dilute caustic solutions. PA polyester polyols have been used in polyurethane/polyisocyanurate rigid foams to impart low thermal conductivity, to lower cost and to lower blowing agent usage as reported in U.S. Pat. No. 4,791,148 to Riley et al., issued Dec. 13, 1988; U.S. Pat. No. 4,888, 365 to Riley et al., issued Dec. 19, 1989 and U.S. Pat. No. 5,164,422 to Londrigan et al., issued Nov. 17, 1992. The PA based polyester polyols have been used in the preparation of urethane-modified isocyanurate foam as reported in U.S. Pat. No. 4,544,679 to Tideswell et al., issued Oct. 1, 1985.
Rigid foams have incorporated PA-based polyester polyols and perfluorinated hydrocarbons to enhance the thermal insulating properties of the foam as reported in U.S. Pat. No. 4,981,879 to Snider. issued Jan. 1, 1991 and EP 394736 A2, Snider et al., Oct. 31, 1990. The preparation of urethane prepolymers utilizing conventional polyester and polyether polyols is disclosed in U.S. Pat. No. 5,021,507 to Stanley et al., issued Jun. 4, 1991, and more recently in U.S. 5,863,980 to Choi et al., issued Jan. 26, 1999.
From a preparation perspective, the use of double metal cyanide catalysts in the manufacture of various polyols is well-established in the art. For example, U.S. Pat. No. 3,829,505, assigned to General Tire & Rubber Company, discloses the preparation of high molecular weight diols, diols etc., using these catalysts. The polyols prepared using these catalysts can be fabricated to have a higher molecular weight and a lower amount of end group unsaturation than can be prepared using commonly-used KOH catalysts. The '505 patent discloses that these high molecular weight polyol products are useful in the preparation of nonionic surface active agents, lubricants and coolants, textile sizes, packaging films, as well as in the preparation of solid or flexible polyurethanes by reaction with polyisocyanates. For other double metal cyanide catalyst usage in the polyol context, see for example, U.S. Pat. Nos. 4,985,491 (to Olin Corp., issued Jan. 15, 1991); and U.S. Pat. No. 4,77,589 (to Shell Oil Company, issued Oct. 16, 1984).
The polymerization of epoxides such as propylene oxide or mixtures of propylene oxide and ethylene oxide using water and/or alcohols as initiators is also of great industrial importance since the resulting polyether alcohols or polyether polyols are very versatile compounds which can be used as such or as intermediates In the manufacture of various products such as (flexible) polyurethanes, detergents, oil additives and brake fluids.
The polymerization of epoxides is normally carried out under basic conditions, i.e. by using potassium hydroxide or sodium hydroxide as a catalyst. Although products (polyether polyols or polyether alcohols) of good quality can be obtained, the use of these inorganic bases limits the capacity of the process since a long batch time is required to warrent good quality products. Shortening the batch times is not readily achievable by simply using more catalyst, as such increased usage would impose an unacceptable and significant increase in monetary costs. Shortening of the batch time is not however impossible, but it has the intrinsic disadvantage that the selectivity of the process is decreased substantially, which seriously affects the product properties.
Therefore, alternative catalytic systems allowing in principle a shorter batch time have already been proposed in the art. Reference is made in this respect to double metal cyanide complexes such as are disclosed in British Patent Specification No. 1,149,726 (for instance zinc hexacyanometallate complexes also containing zinc chloride, water and an organic ligand) and in East German Patent Specification No. 148,957 (specifically metal hexacyano-iridium complexes also containing zinc chloride, water and an ether).
As mentioned above, both polyester-based and polyether-based polyols have their respective beneficial properties and drawbacks/limitations. Additionally, and perhaps most importantly, polyether and polyester polyols are generally not compatible with each other, i.e., they are often not readily soluble or miscible, and therefore are not readily capable of being employed as a mixture for use in any particular application. An ideal polyol would have the desirable properties exhibited by both ester- and ether-based polyols, with limited disadvantages of each previously mentioned. Additionally, and most importantly, there has been a long felt need for a polyol which can function as either a primary polyol or co-polyol in urethane and urethane prepolymer applications and/or compatibilize, i.e. solubilize, reduce viscosity, and make miscible, mixtures of conventional polyester and polyether polyols.